fix: handle all CSS newline types in CSSSourceCode

[sethamus]

Prerequisites checklist

• I have read the contributing guidelines.

What did you do?

a {\r/* CR */\f/* FF */\n/* LF */\r\n/* CRLF */}

What did you expect to happen?

• CSSSourceCode.lines returns the correct array of lines.
• getLocFromIndex and getIndexFromLoc return correct line/column positions.

What actually happened?

Lines containing CR or FF were not split, causing incorrect line/column calculations.

What is the purpose of this pull request?

According to the CSS Syntax Module Level 3, CSS defines newline as one of:

• Line Feed (\n)
• Carriage Return + Line Feed (\r\n)
• Carriage Return (\r)
• Form Feed (\f)

CSSSourceCode previously only handled LF and CRLF correctly because it relied on the default lineEndingPattern from TextSourceCodeBase (/\r?\n/).

This PR ensures CSSSourceCode aligns with the CSS specification for newline handling.

What changes did you make? (Give an overview)

• Updated CSSSourceCode to pass lineEndingPattern: /\r\n|[\r\n\f]/u to TextSourceCodeBase.
• Added tests to verify correct behavior for LF, CRLF, CR, FF.

Related Issues

fixes #276

Is there anything you'd like reviewers to focus on?

[nzakas]

LGTM. Thanks!